The ongoing evolution of microcircuit design has focused on the speed and size of electrical integrated circuit (IC) components, typically in a silicon chip. IC designers have continuously strived to make the IC faster and more functional while taking up less chip space. Currently, interconnection technology is considered as one of several areas that may be advanced to both increase the speed of the IC and to decrease the size of the chip.
For example, only a few years ago spacing between adjoining circuit elements in a typical IC was in the neighborhood of two to three microns. Today, many ICs are being designed at spacing distances as small as 0.35 microns or less. To accommodate narrower spacing and the increased functionality, more layers of conductors are formed above the substrate of the IC, to achieve the necessary number of electrical connections between the more densely located functional elements formed on the substrate of the IC. Advances in fabrication techniques allow as many as five or more separate horizontal layers of interconnect conductors.
Optical waveguides are sometimes considered as replacements or enhancements over the common metal conductors in IC-like structures. Optical signals allow the functional components to operate more quickly or at a higher speed, and unlike electrical signals, optical signals are usually not susceptible to noise and interference. In general, optical signal conduction, with its reduced susceptibility to noise and interference, obtains increased speed in data transmission and processing. Furthermore, due to the coherent nature of laser optical signals and their reduced susceptibility to noise, many more optical signals can be routed in one waveguide or layer of waveguides than is possible using conventional electrical signal interconnect conductors. Therefore, an IC-like structure incorporating optical interconnect waveguides may offer advantages in IC-like structures.
Because of the benefits from optical waveguides, the emphasis on more functionality from smaller sized devices, and the knowledge gained from the development of electrical ICs, it is expected that the evolution of IC-like structures which use waveguides to conduct optical signals will parallel the evolution of electrical ICs . With this historical perspective in mind, IC-like structures which partially or exclusively employ optical waveguides as interconnects are expected to be structured with multiple layers of interconnect waveguides.
The typical optical interconnection is a single waveguide or channel between the two components. In general, the waveguide defines a straight conductive path between conversion devices which convert electrical signals to optical signals and convert optical signals to electrical signals.
A space-effective physical placement and integration of various functional components in an IC-like structure requires considerable flexibility in routing the interconnects. Unfortunately, straight waveguides will not accommodate bends or corners since light signals do not travel around corners. Once a signal propagates the length of the channel, a directional coupler is used to redirect the signal if a change in direction is desired. Directional couplers may substantially increase the manufacturing cost of the IC-like structure, may make effective optical circuit layout impossible or impractical, and may result in a larger IC-like structure.
The previously mentioned patent application relating to the On-Chip Single Layer Horizontal Deflecting Optical Waveguide describes a waveguide and a method of manufacturing it which allow the waveguide to be bent in a horizontal plane. This improvement significantly increases the flexibility and routing of optical waveguides, allowing them to be routed and laid out in an IC-like structure to accommodate greater densities of functional components. However, to fully achieve the densities of functional components in IC-like structures, it will be necessary to also route optical signals from one horizontal layer of optical waveguides into a vertically adjoining horizontal layer of optical waveguides. Similar vertical routing of electrical signals has also been utilized effectively in higher density electrical ICs. However, there is no known previous technique for routing optical signals vertically between horizontal layers of optical waveguide interconnects within the interior of an IC-like structure.
It is with respect to these and other issues that the present invention has evolved.